As you may know if you've read my other How To blog posts, I use PowerPoint to do much of my designing. It's super silly in some ways, but it is because I am comfortable with the tools and it is a nearly universal software that most people have. What I'll describe here is a pretty easy process that doesn't require much artistic ability, just a lot of patience and diligence. We'll first create a basic transparent grid of one color, use a silhouette graphic for reference, and then "trace" the reference graphic by filling some of the squares a different color.
1. To start, open up a new, blank presentation. Draw a square by using the rectangle tool and holding down Shift to ensure the height and width are equal. Make it relatively small, since you'll be making a lot of these. Mine ended up being 0.26" by 0.26".
2. Use the Format Shape options to choose the color you want as the background color for your design.
3. Increase the Transparency of the Fill to about 32%. This is really important, so you'll be able to see the reference image later.
4. Add a Solid line that will be visible as well, this well help you see the borders of each shape, both when you're duplicating them and creating the grid, and later when you're drawing your silhouette. I used 1.75 pt Width and a 
fairly dark color.
5. Now, we get to the tedious copy and paste steps. A word of warning, it is worth spending the time to make sure the lines are very straight and lined up here. Copy the square and paste it. PowerPoint will put the new square slightly offset.
6. Grab that new square and drag it next to the first one. Automatic guidelines will temporarily appear and 
help you ensure that it matches the alignment of the first square. When you're satisfied, release the mouse. If you're not happy with the alignment, you can click on it and move it again, or use the arrow keys on your keyboard to adjust slightly.
7. When you're happy with that alignment, copy both squares and paste, to make a 2x2 square. You'll notice the guidelines will disappear if they're not well aligned and will re-appear when they are aligned.
8. Keep copying and pasting bigger and bigger rectangles or squares until you have the desired size (you can keep track of this by making a 2x2, then 4x4, then 8x8, etc). I chose a 32 x 32 grid because that's one of the sizes for the base plates, so that would be 
easy to mount because it doesn't require additional plates. For reference, the Lego art pieces are 48 x 48. If you plan to purchase one of those sets in order to re-purpose the frames and pieces, then you'll want to make your grid 48 x 48 to match. Another note: when you have the top half, if it looks like you're going to exceed the size of the slide, you may want to slide the whole grid up slightly above the slide so that the bottom portion doesn't try to snap to the edge of the slide.
9. Now, if you don't have a reference graphic you want to emulate already, use Google Images and search for the topic you're interested in and use the word "silhouette" in search if needed. Ideally, look for a simple graphic with a white or transparent background and a black or very dark graphic.
10. Copy and paste the image into a new slide and enlarge it if needed. Use the
11. Remove Background feature if needed to remove distracting things in the background. If the silhouette is the wrong color and you can find a good graphic to use that has the right color, you can also utilize the Color and Corrections tools in PowerPoint to make white outlines black, etc.
12. Copy the updated graphic to the slide with your grid. Adjust the size of the reference graphic to fit in the grid but also to take up as much space as possible in the grid.
13. If the "shape" containing the graphic isn't extending beyond the grid, it's a good idea to use the Crop tool to actually extend the shape. This will allow you to select the graphic to delete it later.
14. It's also a good idea to make a copy of this finished reference graphic to a blank slide just in case.
15. Now, go back to the slide with the grid and the reference silhouette graphic. Right-click on the reference graphic and select "Send to Back". Since you made the fill of the squares transparent, you should see the silhouette still coming through but less clear.
16. Select just one box in the grid which is showing inside the silhouette, and change the color to whatever you want to use as your foreground. In the example, I just used white as my foreground color, but because it still has the transparency setting, it looks grey because the reference graphic is black. This is fine for now, you'll see it more clearly later.
17. As much fun as selecting each box and changing the fill each time would be, there is a REALLY helpful tool here that's going to make this a bit faster: the Format Painter. If you've never used the Format Painter before, now's the time to learn. First, click the newly colored square (the white square in my example), then Double-Click on Format Painter. Now, every square you click will turn that color (and take on all formatting) until you either click outside of the shapes or hit Esc on your keyboard. Be sure not to hit your reference graphic (use Undo if you do).
18. Using this tool, you can start "coloring" the area that your silhouette shows. Don't worry if you go too far, you can always use the Format Painter to go back over squares you want to change back. Keep "coloring" until your silhouette is mostly traced / covered. If you want to see how it looks or check your technique, you hit Esc on your keyboard and delete the reference silhouette graphic - your art is taking shape! Use Undo to put it back in place.
19. If you do other steps before putting it back, use the copy of the graphic you made on the other slide, copy and paste it back on your main working slide and then use the "Send to Back" function again.
20. When you're happy with your "colored" pattern, delete the reference silhouette graphic and then select all of the squares and change the line to "No Line". This will give you a better view of what it will look like. Use Undo or add the solid lines back to use for a template.
Voila! You now have a template for making your own custom Lego art. Time to go to the Lego Store for Pick-a-Brick or order online to get the pieces you need.
What are you going to create? Post pictures in the comments!
My finished product shown here, I added a sun behind my palm tree and used regular white bricks instead of the circles for the palm tree and frame. I needed the purple and yellow dots from two Marilyn Monroe sets and two 32x32 white baseplates to make this.
Pro-tip: Employ kids or significant others to help you out by defining so-many rows or columns that are one solid color, to lighten your load. Using my palm tree example, I had 9 columns on one side and 4 columns on the other side that were going to be all the same color, as highlighted in darker blue here. You can use painter's tape to tape over the area you don't want them to place bricks on, if needed.
Update: I made a second one in different colors!
Here's another example of a simple custom Lego Mosaic piece I created for a giraffe with sunglasses:
I used this AI-generated graphic as the inspiration:
Here's the final art:
For more complex graphics, this website is a great, free way to generate instructions: https://lego-art-remix.com/
Note that in Step 1 under Resolution, you can input the size of your canvas.
